Planets - Zoom Astronomy Your age on the Planets The Planets (plus the Dwarf Planet Pluto) Our solar system consists of the sun, eight planets, moons, many dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The sun is the center of our solar system ; the planets, their moons, a belt of asteroids , comets , and other rocks and gas orbit the sun. The eight planets that orbit the sun are (in order from the sun): Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune . Another large body is Pluto , now classified as a dwarf planet or plutoid. A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane, the ecliptic (Pluto is an exception; it has an elliptical orbit tilted over 17° from the ecliptic).

Easy ways to remember the order of the planets (plus Pluto) are the mnemonics: "My Very Excellent Mother Just Sent Us Nine Pizzas" and "My Very Easy Method Just Simplifies Us Naming Planets" The first letter of each of these words represents a planet - in the correct order. The largest planet is Jupiter. It is followed by Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury, and finally, tiny Pluto (the largest of the dwarf planets). Jupiter is so big that all the other planets could fit inside it. The Inner Planets vs. the Outer Planets The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun). The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons. The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet). They are mostly huge, mostly gaseous, ringed, and have many moons (again, the exception is Pluto, the dwarf planet, which is small, rocky, and has four moons).

Temperatures on the Planets Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere. Density of the Planets The outer, gaseous planets are much less dense than the inner, rocky planets. The Earth is the densest planet. Saturn is the least dense planet; it would float on water. The Mass of the Planets Jupiter is by far the most massive planet; Saturn trails it. Uranus, Neptune, Earth, Venus, Mars, and Pluto are orders of magnitude less massive. Gravitational Forces on the Planets The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared. A Day on Each of the Planets A day is the length of time that it takes a planet to rotate on its axis (360°). A day on Earth takes almost 24 hours.

The planet with the longest day is Venus ; a day on Venus takes 243 Earth days. (A day on Venus is longer than its year; a year on Venus takes only 224.7 Earth days). The planet with the shortest day is Jupiter ; a day on Jupiter only takes 9.8 Earth hours! When you observe Jupiter from Earth, you can see some of its features change. The Average Orbital Speed of the Planets As the planets orbit the Sun , they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion ). The Planets in Our Solar System Planet (or Dwarf Planet) In 2005, a large object beyond Pluto was observed in the Kuiper belt. A few astronomers think that there might be another planet or companion star orbiting the Sun far beyond the orbit of Pluto. This distant planet/companion star may or may not exist. The hypothesized origin of this hypothetical object is that a celestial object, perhaps a hard-to-detect cool, brown dwarf star (called Nemesis ), was captured by the Sun's gravitational field.

This planet is hypothesized to exist because of the unexplained clumping of some long-period comet's orbits. The orbits of these far-reaching comets seem to be affected by the gravitational pull of a distant, Sun-orbiting object. Planet Activities and Quizzes Planetary Size and Distance Comparison - National Geographic Society Planetary Size and Distance Comparison What is the diameter and relative distance from the sun of each planet in our solar system? This lists the logos of programs or partners of NG Education which have provided or contributed the content on this page. Program Tips & Modifications Modification If you do not have enough space to do the kinesthetic model, you can modify this activity to have students create a string-and-bead solar system model in the classroom by converting astronomical units to a 10 centimeter/AU (4 inch) scale. Students will need a string 4.5 meters long. Have students tie beads in place to represent planetary distances.

Sun 0.0 AU=0 cm Mercury 0.4 AU=4 cm Venus 0.7 AU=7 cm Earth 1.0 AU=10 cm Mars 1.5 AU=15 cm Asteroid Belt 2.8 AU=28 cm Jupiter 5.2 AU=52 cm Saturn 9.6 AU=96 cm Uranus 19.2 AU=192 cm Neptune 30.0 AU=300 cm Tip Make sure students understand that these are only models or visualizations of the relative distances between the planets and the sun. Planets all orbit the sun at different velocities, so they rarely form a straight line from the sun. Instead, they appear somewhere along their orbital paths. 1. Review planet order and relative sizes in our solar system . Display the NASA illustration: All Planet Sizes. Ask students to point out the location of Earth. Then challenge them to identify all of the planets, outward from the sun (left to right): inner planets Mercury, Venus, Earth, Mars; outer planets Jupiter, Saturn, Uranus, Neptune, and Pluto.

Remind students that Pluto is no longer considered a planet in our solar system; it was downgraded to the status of dwarf planet in 2006. Point out the locations of the asteroid belt (between Mars and Jupiter) and Kuiper belt (past Pluto) if they were included in this illustration. Explain to students that the illustration shows the planets in relative size . Ask: What do you think relative size means? Elicit from students that the pictures show how big the planets are when compared to each other and to the sun. Ask: Which planet is the smallest? (Mercury) Which is the largest? (Jupiter) 2. Have students gather data and compare planet sizes. Divide students into small groups. Distribute one copy of the worksheet Planetary Size Comparison to each group. Have groups use the Planet Size Comparison interactive to find and record data on planet diameters and ratios. Ask: What do you notice about the size of the planets? (Possible response: The inner, rocky planets are smaller than the outer, gaseous planets.) How do you think the sizes of the planets compare? (Possible response: There is a big difference in the sizes of the planets.

Some are fairly small and others are extremely large.) Would it be easy to model the planet sizes? Why or why not? (Possible response: No, because of the great differences in size.) How could we model differences? What everyday objects could represent planets and the sun? (Possible responses: peas/beach ball; grains of sand/orange) Have students discuss the answers in their small groups. Then regroup as a class to discuss students’ ideas. 3. Build background about the astronomical unit (AU). Explain to students that an astronomical unit, or AU, is a simplified number used to describe a planet’s distance from the sun. It is a unit of length equal to the average distance from Earth to sun, approximately 149,600,000 kilometers (92,957,000 miles). Only Earth can be assigned AU 1. Planets farther away would have AU greater than 1; planets closer would have AU less than 1. Ask: Why do you think scientists find it helpful to use astronomical units? (Possible response: Distances in the solar system are very large.

Using AU helps keep the numbers manageable, or smaller, so we can easily calculate very large distances.) What are the challenges of using kilometers or miles instead? (Possible response: Using kilometers or miles would make calculations more difficult and could produce errors in measurements required to accurately send a probe or lander to another planet.) Explain to students that the astronomical unit provides a way to express and relate distances of objects in the solar system and to carry out astronomical calculations. For example, stating that the planet Jupiter is 5.2 AU (5.2 Earth distances) from the sun and that Pluto is nearly 40 AU allows you to more easily compare the distances of all three bodies. 4. Introduce the modeling activity. Tell students that they are going to stand in for the planets and planetary objects in order to create a model of relative planetary sizes and relative distance s. Display the NASA illustration: How Big is the Sun? to give students a sense of the relative sizes of planets compared to an everyday object like a basketball. Make sure students understand that the distances between the planets are very large compared to the sizes of each planet. This makes it extremely difficult to create an exact scale of our solar system, so this activity will focus on the distance comparison. 5.

Have groups create models of relative planetary distances. Divide students into groups of 9, 10 or 11, depending on class size. (If 9, one student represents the sun and the remaining students represent 8 planets; If 10, the sun, planets, and asteroid belt; If 11, the sun, planets, asteroid belt, and Kuiper Belts) Take students to a large area, such as the gymnasium or empty parking lot.

You’ll need enough space for each group to spread out and create their model, using the following scale, with each step equaling approximately 1 meter (about 3.28 feet): Sun: stands at the edge of the area Mercury = 1 step from sun Venus = 2 steps from sun Earth = 2.5 steps from sun Mars = 4 steps from sun Asteroid belt = 8 steps from sun Jupiter = 13 steps from sun Saturn = 24 steps from sun Uranus = 49 steps from sun Neptune = 76 steps from sun Kuiper belt = 100 steps from sun Emphasize that at this scale, the sun would be less than 1.3 centimeters (0.5 inches) in diameter . Ask students to describe what they notice about planetary distances from the model. If needed, allow one student from each group to put an object in their place and walk around their group’s model to make observations. 6. Have students make a math connection. Distribute copies of the worksheet Stepping Out the Solar System to each group. Have students recalculate the number of paces for each planet’s orbit, as constrained by the size of the available area.

Use the provided answer key to check groups’ work. Then have students recreate the model. Informal Assessment Have students work independently to summarize, in writing, what they learned about our solar system, including: locations of planets in relation to the sun and one another relative sizes of planets, including Earth relative distances of planets any conclusions they can draw about the locations of the asteroid belt and Kuiper belt Extending the Learning Encourage students to practice backyard astronomy. At certain times of day and year, it's possible to view planets Mercury, Venus, Mars, Jupiter, and Saturn with the naked eye. Students can use Sky and Telescope Magazine's Sky at a Glance feature to find out what planets are visible in the night sky and where to look. Ask students to report back to the class with what they observed. Subjects & Disciplines User Permissions For information on user permissions, please read our Terms of Service . If you have questions about licensing content on this page, please contact natgeocreative@ngs.org for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please visit our FAQ page .

Media Some media assets (videos, photos, audio recordings and PDFs) can be downloaded and used outside the National Geographic website according to the Terms of Service . If a media asset is downloadable, a download button appears in the lower right hand corner ( ) of the media viewer. If no button appears, you cannot download or save the media. Text Text on this page is printable and can be used according to our Terms of Service . Interactives Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Earth Facts - Planet Earth - Earth For Kids It is the only planet in the solar system that has life. The Earth is the only inner planet ( Mercury , Venus , Earth and Mars ) to have one large satellite, the Moon . Mars has two very tiny moons. Mercury and Venus have none. The Earth is fragile. Its surface is split into plates (tectonic plates) which float on a rocky mantle – the layer between the surface of the earth, its crust, and its hot liquid core. The inside of the Earth is active and earthquakes , volcanoes and mountain building takes place along the boundaries of the tectonic plates.

As a result of the Earth’s geological activity (the volcanoes and earthquakes) the surface of the Earth has far fewer craters than the surface of planets such as Mars, Venus and Mercury or the surface of the Moon. The craters have sunk down or been worn away by wind and rain over millions of years. When viewed from outer space much of the Earth’s surface cannot be seen because of clouds of water vapour. The water vapour makes the Earth, when seen from outside, into a brilliant shining orb, as you can see in Figure 1. Figure 1. Earth taken from the Apollo 17 spacecraft in 1972 The Earth is the third planet from the Sun and comes between the planet Venus and the planet Mars. Figure 2. The planets of the Solar System. The Earth takes 365¼ days to complete its orbit round the Sun. The Earth’s year is therefore 365 days long but the ¼ days are added up and every fourth year has one extra day, on the 29th of February.

This fourth year is called a Leap Year (366 days) and is always a year which can be divided exactly by 4 – 2000, 2004, 2008, 2012, 2016. The planets closer to the Sun, Mercury and Venus, have shorter years than the Earth. The planets further away from the Sun have longer years; Pluto takes 249 of our years to make one orbit of the Sun. As the Earth orbits round the Sun it turns on its axis, rotating right round in 24 hours. The side of the Earth that faces the Sun has daytime and the side of the Earth that is turned away from the Sun has night-time. When it is daytime in Britain, it is night-time on the opposite side of the Earth in New Zealand. As the Earth orbits round the Sun it tilts very slightly and so gives us the seasons. When the Earth has tilted so that the northern half of the Earth is a little away from the Sun, the northern hemisphere (meaning half of the Earth’s sphere) has winter. At this time the southern hemisphere is tilted very slightly towards the Sun and the southern hemisphere has summer.

Winter in Britain means summer in New Zealand. Closer to the Equator there is much less difference between summer and winter. The Earth is 93 million miles, or 150 million kilometres from the Sun. We can also say that the Earth is 1 AU from the Sun. Astronomers (people who study the planets and stars) use a measurement called an Astronomical Unit, AU. Earth’s measurements are taken as the standard for this system, so Earth is 1 AU from the Sun, Venus is 0.72 AU from the Sun and Mars is 1.52 AU from the Sun. Pluto, furthest out, is 39.5 AU from the Sun. How many million miles from the Sun is Pluto? The Earth’s diameter, the distance round its middle at the Equator, is 7928 miles, or 12760 kilometres. The Earth is not an exact sphere; the diameter going round the North and South Poles is slightly less than the diameter round the Equator. The Polar diameter is 7891 miles, or 12700 kilometres.

(Try measuring the different diameters of an orange and you will see how they can differ). The Earth is larger than Mercury, Venus and Mars, the planets closest to it. On astronomy maps it often looks smaller than Venus because Venus is shown with a thick layer of sulphuric acid which lies 40 miles above the The Earth differs from all the other planets because it has such a wide diversity of life and intelligent beings. This has only been possible because of the Earth’s atmosphere which has protected the Earth and allowed life to flourish. Useful Websites The Solar System The Solar System Our Solar System is an amazing place. Not only is it home to eight planets, it also hold several dwarf planets, hundreds of moons, and thousands of stars and asteroids. The eight planets in our Solar System are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets orbit the Sun. Here is a funny song to help you remember the planets The Sun The Sun is the center of our Solar System. It is because of the Sun that our solar system gets its name. Sol is the Roman name for Sun. The Sun is the largest object within the Solar System - it makes up more than 95% of all the matter!

It is because of the Sun's large size that the rest of the objects within the Solar System orbit around it. The Sun is very, very hot. It is 10,000 degrees Fahrenheit on its surface. Mercury Mercury is the closest planet to the Sun, making it the first planet in the Solar System. It is named after the Roman messenger god. In mythology, the god was known for being quick - Mercury is the fastest of all the planets to orbit the Sun, because it has the smallest route it has to take! Mercury can occasionally be seen from Earth Mercury is the second densest planet in the Solar System It is mainly made up of iron There is no atmosphere on Mercury Despite its fast trip around the Sun, Mercury's revolution is very slow - one day on Mercury equals about 59 days on Earth! Venus Venus is the second planet from the Sun. It is named after the Roman goddess of beauty and love. Venus is almost the same size as Earth, but other than size the two planets are very different! Fun Facts about Venus Venus appears to be the brightest planet in the sky due to the reflection of the Sun from its clouds, and its closeness to Earth Venus has an incredibly thick atmosphere.

This makes it the hottest of the inner planets Venus rotates East to West Venus is covered in volcanoes Venus does not have any moons Earth Earth is the only known planet that has any life forms in the Solar System. It is the third planet from the Sun. It is the only planet that is not named after a god. Most of the Earth is covered in water - 70%! Earth has a thin atmosphere, that protects us from dangerous gasses and heat in space Earth is the largest of the inner planets Air, water, and land make up the Earth Earth's axis is tilted at 23.5 degrees This a video showing the many different life forms that Earth has Mars Mars is the fourth planet from the Sun. Named for the Roman god of war, it is also known as the "Red Planet". It is the last of the inner planets. Temperatures on Mars are very similar to temperatures on Earth It is believed that Mars once had water on its surface Mars is called the red planet because its surface is covered in red dust The largest volcano in the Solar System is on Mars. It is called Olympus Mons Mars has two small moons Jupiter Jupiter is the first of the outer planets, and the fifth planet from the Sun.

It is named for the king of the Roman gods. It is the largest of all of the planets. Fun Facts about Jupiter Jupiter is best known for its "Great Red Spot" - a mass of hurricanes that have been storming for hundreds of years. The spot is larger in size than that of Earth Jupiter is made up of gasses - there is no solid surface on it Jupiter is so big; Earth could fit inside of it more than 1,000 times! Jupiter has over 50 moons. Four of these moons are as big as planets Jupiter has the most active volcanic activity in the Solar System Learn more about the Great Red Spot! Saturn Saturn is the sixth planet from the Sun. It is named for the Roman god of agriculture. It is most well known for its highly visible rings. Other Features of the Solar System There are many other exciting elements in the Solar System. Here are a few. Asteroids Asteroids are rocky bodies in the Solar System that are too small to be considered actual planets. In between Mars and Jupiter lies the Asteroid Belt, containing well over 90,000 asteroids. Comets Comets are ice and rock that grow tails the closer they get to the sun.

The hotter they get, the longer this "tail" becomes. The sunlight makes comets glow, which causes them to be visible on Earth. Dwarf Planets Dwarf planets are bodies that orbit the sun that are not considered large enough to be actual planets. The most famous dwarf planet is Pluto, which was considered an actual planet up until 2006. Satellites Satellites are machines put into the Solar System by scientists in order to find out more about the Solar System, and what is in it. These machines take pictures, perform experiments, take data, and much, much more. Without them, we wouldn't have the vast amount of information that we have today. Summary The Solar System is a fascinating place. Each of the eight planets have their own unique features, but are also similar in some ways - much like people! It is amazing to think that the Solar System has been around for more than 4.6 billions years. Each of the eight planets orbits the sun in the same direction, and in their own time. We have so much more we can learn about the Solar System, and so much we have learned already today. sit this page to learn more interesting facts about the Solar System!

Want to get an idea of how far apart the planets are? Click here! Resources Our Solar System. Retrieved from Solar System. Retrieved from Solar System Planets: Order of the 8 (or 9) Planets Solar System Planets: Order of the 8 (or 9) Planets By Robert Roy Britt | January 22, 2016 12:35pm ET MORE The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale. Credit: NASA Ever since the discovery of Pluto in 1930, kids grew up learning about the nine planets of our solar system. That all changed starting in the late 1990s, when astronomers began to argue about whether Pluto was a planet. In a highly controversial decision , the International Astronomical Union ultimately decided in 2006 to call Pluto a “dwarf planet,” reducing the list of “real planets” in our solar system to eight. However, astronomers are now hunting for another planet in our solar system, a true ninth planet , after evidence of its existence was unveiled on Jan. 20, 2016.

The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. [ Solar System Pictures: A Photo Tour ] If you insist on including Pluto , then that world would come after Neptune on the list; Pluto is truly way out there, and on a wildly tilted, elliptical orbit (two of the several reasons it got demoted). Interestingly, Pluto used to be the eighth planet, actually. More on that below. Terrestrial planets The inner four worlds are called “ terrestrial planets ,” because, like Earth, their surfaces are all rocky. Pluto, too, has a solid surface (and a very frozen one) but has never been grouped with the four terrestrials. Jovian planets The four large outer worlds — Jupiter, Saturn, Uranus, and Neptune — are known as the “Jovian planets” (meaning “Jupiter-like”) because they are all huge compared to the terrestrial planets, and because they are gaseous in nature rather than having rocky surfaces (though some or all of them may have solid cores, astronomers say).

According to NASA , "two of the outer planets beyond the orbit of Mars — Jupiter and Saturn — are known as gas giants; the more distant Uranus and Neptune are called ice giants." This is because, while the first two are dominated by gas, while the last two have more ice. All four contain mostly hydrogen and helium. Dwarf planets The IAU definition of a full-fledged planet goes like this: A body that circles the sun without being some other object's satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has "cleared its neighborhood" of most other orbiting bodies. Yeah, that’s a mouthful. The problem for Pluto, besides its small size and offbeat orbit, is that it shares its space with lots of other objects in the Kuiper Belt , beyond Neptune. Still, the demotion of Pluto remains controversial . The IAU planet definition puts other small, round worlds in the dwarf planet category, including the Kuiper Belt objects Eris , Haumea , and Makemake . Also now a dwarf planet is Ceres , a round object in the Asteroid Belt between Mars and Jupiter.

Ceres was actually considered a planet when discovered in 1801 and then later deemed to be an asteroid. Some astronomers like to consider Ceres as a 10th planet (not to be confused with Nibiru or Planet X ), but that line of thinking opens up the possibility of there being 13 planets, with more bound to be discovered. The planets Below is a brief overview of the eight primary planets in our solar system , in order from the inner solar system outward: Mercury The closest planet to the sun, Mercury is only a bit larger than Earth's moon. Its day side is scorched by the sun and can reach 840 degrees Fahrenheit (450 Celsius), but on the night side, temperatures drop to hundreds of degrees below freezing. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon. Over its four-year mission, NASA's MESSENGER spacecraft has revealed views of the planet that have challenged astronomers' expectations.

Discovery: Known to the ancients and visible to the naked eye Named for: Messenger of the Roman gods Diameter: 3,031 miles (4,878 km) Orbit: 88 Earth days Venus' southern hemisphere, as seen in the ultraviolet. Credit: ESA Venus The second planet from the sun, Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth, Venus' thick, toxic atmosphere traps heat in a runaway "greenhouse effect." Oddly, Venus spins slowly in the opposite direction of most planets. The Greeks believed Venus was two different objects — one in the morning sky and another in the evening. Because it is often brighter than any other object in the sky — except for the sun and moon — Venus has generated many UFO reports.

Discovery: Known to the ancients and visible to the naked eye Named for: Roman goddess of love and beauty Diameter: 7,521 miles (12,104 km) Orbit: 225 Earth days An image of the Earth taken by the Russian weather satellite Elektro-L No.1. Credit: NTsOMZ Earth The third planet from the sun, Earth is a waterworld, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface rotates about its axis at 1,532 feet per second (467 meters per second) — slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second).

Diameter: 7,926 miles (12,760 km) Orbit: 365.24 days Day: 23 hours, 56 minutes Related: Mars researchers are focusing both Earth-based and planet orbiting sensors to better understand sources of methane on the red planet. Image Credit: Space Telescope Science Institute Mars The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And Mars harbors water ice. Scientists think it was once wet and warm, though today it’s cold and desert-like. Mars' atmosphere is too thin for liquid water to exist on the surface for any length of time. Scientists think ancient Mars would have had the conditions to support life, and there is hope that signs of past life — possibly even present biology — may exist on the Red Planet.

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of war Diameter: 4,217 miles (6,787 km) Orbit: 687 Earth days Day: Just more than one Earth day (24 hours, 37 minutes) Related: Close-up of Jupiter's Great Red Spot as seen by a Voyager spacecraft. Credit: NASA/JPL-Caltech Jupiter The fifth planet from the sun, Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.

Discovery: Known to the ancients and visible to the naked eye Named for: Ruler of the Roman gods Diameter: 86,881 miles (139,822 km) Orbit: 11.9 Earth years The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the Cassini Division in this natural color image taken as Saturn approaches its August 2009 equinox. Credit: NASA/JPL/Space Science Institute Saturn The sixth planet from the sun is known most for its rings . When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings. The rings are made of ice and rock. Scientists are not yet sure how they formed. The gaseous planet is mostly hydrogen and helium. It has numerous moons .

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of agriculture Diameter: 74,900 miles (120,500 km) Orbit: 29.5 Earth years Day: About 10.5 Earth hours Related: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which the planet is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory Uranus The seventh planet from the sun, Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit — it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt. The tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years. Uranus is about the same size as Neptune. Methane in the atmosphere gives Uranus its blue-green tint. It has numerous moons and faint rings.

Discovery: 1781 by William Herschel (was thought previously to be a star) Named for: Personification of heaven in ancient myth Diameter: 31,763 miles (51,120 km) Orbit: 84 Earth years Neptune’s winds travel at more than 1,500 mph, and are the fastest planetary winds in the solar system. Credit: NASA/JPL Neptune The eighth planet from the sun, Neptune is known for strong winds — sometimes faster than the speed of sound. Neptune is far out and cold. The planet is more than 30 times as far from the sun as Earth. It has a rocky core. Neptune was the first planet to be predicted to exist by using math, before it was detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth. Discovery: 1846 Pluto and its moons orbit the sun near the edge of our solar system.

Learn all about Pluto's weirdly eccentric orbit, four moons and more in this Space.com infographic . Credit: SPACE.com/Karl Tate Pluto (Dwarf Planet) Once the ninth planet from the sun, Pluto is unlike other planets in many respects. It is smaller than Earth's moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune's path and once again became the solar system's most distant planet — until it was demoted to dwarf planet status. Pluto will stay beyond Neptune for 228 years. Pluto’s orbit is tilted to the main plane of the solar system — where the other planets orbit — by 17.1 degrees. It’s a cold, rocky world with only a very ephemeral atmosphere. NASA's New Horizons mission performed history's first flyby of the Pluto system on July 14, 2015.

[Related: New Horizons' Pluto Flyby: Latest News, Images and Video ] Discovery: 1930 by Clyde Tombaugh Named for: Roman god of the underworld, Hades Diameter: 1,430 miles (2,301 km) Orbit: 248 Earth years NASA Solar System Exploration: Dwarf Planets Planet Nine Planet Nine orbits the sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) The strange world's orbit is about 600 times farther from the sun than the Earth's orbit is from the star. Scientists have not actually seen Planet Nine directly . Its existence was inferred by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy objects left over from the birth of the sun and planets. Mercury In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Mercury has been known since at least the time of the Sumerians (3rd millennium BC). The IAU changed the definition of "planet" so that Pluto no longer qualifies. There are officially only eight planets in our solar system. Of course this change in terminology does not affect what's actually out there. In the end, it's not very important how we classify the various objects in our solar system. What is important is to learn about their physical nature and their histories. Planet Order from the Sun; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune Our knowledge of our solar system is extensive but it is far from complete. Some of the worlds have never even been photographed up close. The Nine Planets is an overview of what we know today. We are still exploring, much more is still to come: We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time. -- T. S. Eliot How far is each planet from Earth? (Intermediate) - Curious About Astronomy? Ask an Astronomer How far is each planet from Earth?

(Intermediate) (Intermediate) >" onclick="window.open(this.href,'win2','status=no,toolbar=no,scrollbars=yes,titlebar=no,menubar=no,resizable=yes,width=640,height=480,directories=no,location=no'); return false;" rel="nofollow"> We get lots of emails asking this, but it's actually a difficult question to answer because the planets are moving in their orbits all the time, and so the distance from each planet to Earth is constantly changing. When both planets are on the same side of the Sun, and form a line with the Sun, then they are closest to each other. When two planets are on opposite sides of the Sun, and form a line with the Sun, then they are farthest away. An inferior planet (a planet whose orbit is interior to Earth's orbit) is farthest from Earth near the time of superior conjunction and closest to Earth near the time of inferior conjunction. The diagram below (from this page ), with Earth as the blue-green dot, shows a gray circle representing an inferior planet (Mercury or Venus) at these places in its orbit.

For superior planets (like Mars), shown as the red circle in the diagram above, the planet is closest to Earth at about the time of opposition, and it is farthest from Earth at about the time of conjunction. However, since the planets' orbits are ellipses (not perfect circles), and they are not in exactly the same plane, the planet's minimum or maximum distance from Earth may not occur at exactly the same time as opposition or conjunction. Usually when people ask this question, what they mean is "What is the distance between the orbit of Earth and the orbit of each planet?" or "What is the closest that each planet comes to Earth?" (These are essentially the same question, because the planets can't get any closer than their orbital spacing allows.) You can compute this in a rough way by assuming that the orbits are circular and coplanar, and looking at the planet-to-Sun distance for each planet. Since the distances are so large, we usually express them in Astronomical Units (AU). (An AU is the average distance from Earth to the Sun, about 150 million kilometers or 93 million miles.) The table below lists the distance of each planet from the Sun in AU.

(Numbers were taken from this page .) Planet Pluto (dwarf planet) 39.48 To find the approximate distance between the orbits of two planets in AU, subtract the two planet-Sun distances. For example, Earth orbits at 1 AU from the Sun and Venus orbits at 0.72 AU from the Sun. The difference between these two distances is 1.00 - 0.72 = 0.28 AU. To get the number in kilometers, multiply by the conversion above: 0.28 × (150 million kilometers) = 42 million kilometers. Another example: Jupiter is 5.2 AU from the Sun and Earth is 1.0 AU from the Sun. So the distance between Jupiter's orbit and Earth's orbit is about 5.2 - 1.0 = 4.2 AU or 630 million kilometers. You can use this process for any of the planets using the numbers above. For completeness, I should point out that the circular orbit assumption is better for some planets than others. For example, Mars has a fairly eccentric elliptical orbit, which means that its "closest-approach" distance changes.

That's why in August 2003 , Mars was closer to Earth than it has been in about 60,000 years. But the numbers above are generally what are used in introductory astronomy classes. And that's why the Earth-Venus distance calculated in the previous paragraph (42 million kilometers) is slightly greater than the actual minimum Earth-Venus distance (38 million kilometers) - the planets' eccentric orbits can allow them to get slightly closer than the distance that one finds from the simple calculation. If you'd like to see which planets are closer to Earth right now, you can look at the Solar System Simulator or Solar System Live websites, where you can choose a time and then look down on the Solar System from above to see where the planets are. If you're technically inclined and want exact numbers, you can use the JPL Horizons system to select a planet, select a time range, and select "Observer range and range-rate" as an output quantity. You will get a list of times along with the Earth-object distance in AU. This page was last updated by Sean Marshall on March 31, 2016.

Outer Space: "We are the Planets," The Solar System Song by StoryBots - YouTube Outer Space: "We are the Planets," The Solar System Song by StoryBots Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. Rating is available when the video has been rented. This feature is not available right now. Please try again later. Published on Aug 2, 2013 Let the StoryBots DJ "revolve" it with sweet beats as the rapping sun and planets give you their spin on the whole solar system. → The StoryBots offer a world of learning and fun for kids and parents! Explore our award-winning apps → Get iPhone & iPad App → The StoryBots are curious little creatures who live beneath our screens, offering a world of learning and fun for kids and parents. From Starring You® videos and books that make your child the star of the show, to rockin' ABC videos, the StoryBots offer a creative collection of web and mobile apps designed to entertain grown-ups as much as kids.

Parents everywhere are summoning the StoryBots to inject a big dose of happiness into their family routine! Get iPhone & iPad App → FACEBOOK: We can see the whole Solar System from here. I think we can hear it from here too. ALL PLANETS (CHORUS) We are the planets of the Solar System Different sizes for every one The music never ends We are such good friends And we all orbit the sun SUN Here comes the Sun rapping first on this track, from the beginning I'm the center of the solar system, planets be spinning Around me, so hot, I'm roasting, ya see? Now I pass the mic to the planet closest to me MERCURY Mercury! The smallest planet, small as Earth's moon (MOON: "Yo!") I get super hot and cold and I spin very slow VENUS I'm Venus!

I've got mountains and volcanoes that spray I'm the same size as Earth but spin the opposite way EARTH Yeah, I'm Earth, I'm the home to every boy and girl (Sung by Stars) Such a beautiful, beautiful world MARS I'm Mars, the red planet, I've got deserts and ice And I've got two moons - nice - that's like one moon, twice! JUPITER I'm Jupiter! the biggest planet, I'm humungous, gargantuan I spin the fastest, rap the fastest, plus I'm handsome, BAM SON!

SATURN Oh please, I'm Saturn, check out my beautiful rings Made up of billions of rocks, dust, and other things URANUS I'm Uranus, I say that with pride, okay, I lied I'm embarrassed 'cause I'm the only planet lying on its side (Uranus lies on its side and the mic flies to Neptune) NEPTUNE I'm Neptune, I'm cold, dark, windy and mysterious I'm very stormy, so bring an umbrella - I'm serious ALL PLANETS (CHORUS) We're the planets in the Solar System Different sizes for every one The music never ends We are such good friends And we all orbit the sun Well, we are done exploring the Solar System. I am thirsty. Let's explore the rest of the Milky Way Galaxy.

ABC Jamboree Playlist: Visit StoryBots.com for more parent and kid fun: Credits: Lyrics by Erik Weiner / Music by Mark Weiner Animation by StoryBots Explore the StoryBots "universe" today: Category The Solar System: Mercury | The Institute for Creation Research The Solar System: Mercury Resources › Physical Sciences Resources › Astronomy The smallest planet of our solar system holds some big mysteries for secular astronomers, and it continues to delight creationists. Mercury is only 38 percent the diameter of Earth, making it the smallest and least massive of the eight planets. It is the innermost planet of the solar system, orbiting the sun at a distance of only 36 million miles. That is nearly three times closer to the sun than Earth is. Mercury is a solid, rocky world, with only a trace of an atmosphere. It has mountains, valleys, plains, and craters—lots and lots of craters! In appearance, Mercury resembles a 40 percent larger (in radius) version of the moon. But when it comes to creation research of the early solar system, Mercury provides many interesting clues. The unusual characteristics of this world make for an intriguing study.

A World of Extremes Since it is closest to the sun, Mercury has the shortest “year” of any planet, taking only 88 Earth days to complete one orbit. So every time Earth completes one orbit, Mercury has already made four trips around the sun. On the other hand, it has the longest solar day of any planet. A hypothetical observer on Mercury’s surface would only see a sunrise every 176 Earth days! The “sidereal” (relative to the stars) rotation rate of Mercury is 59 Earth days. If we could somehow watch Mercury through a telescope from a distant star, we would see it rotate one time every 59 days. This is called a “sidereal day” because sidereal means “star,” and we are watching from the stars in this scenario. On the other hand, if we could somehow watch Mercury from the position of the sun, Mercury would appear to turn once every 176 days. This is called a “solar day.” The reason for the difference is that Mercury orbits the sun as it rotates.1 This is also true of the other planets, though the difference is generally much less.2 Mercury’s slow rotation results in some other interesting effects.

A given spot on Mercury is in direct sunlight for about 88 continuous Earth days at a time. And since Mercury is three times closer to the sun than Earth is, and since there is no substantial atmosphere to transport the heat, the surface temperature on the day side of Mercury can reach 800 degrees Fahrenheit—more than hot enough to melt lead. Perhaps even more surprising is that the temperature on the night side of Mercury can drop to -280 degrees Fahrenheit! This is because it is in continual darkness for up to 88 days and there is no significant atmosphere to prevent the nighttime surface from radiating virtually all its heat into space. These extremes lead to some interesting hypothetical scenarios. Suppose your spaceship ran out of fuel, but not before you were able to land near the equator of Mercury. Thankfully, you have landed on the night side (barely), and your spacesuit protects you from the bitter cold surface. But it won’t protect you from the 800-degree daytime temperatures that are about to occur when the sun rises in just a couple of hours! Thanks to Mercury’s very long day, you could begin jogging west at a leisurely pace of two miles per hour.

As long as you can maintain that pace, you could stay ahead of the sunrise and remain safely in the night for as long as it takes for the rescue ship to arrive. Effectively, you would be jogging in the opposite direction that the planet rotates, and at about the same rate, thereby permanently remaining in the safe shadow of night. Mercury’s Strange Orbit Another curious aspect of Mercury’s rotational (sidereal) period is that it is precisely two thirds of its orbital period. So Mercury turns on its axis three times every time it orbits the sun twice. In astronomy, whenever the ratio of two periods can be expressed by a simple fraction, it is called a “resonance.” Mercury is the only planet in our solar system whose rotation period and orbital period are in resonance. There is a reason for this, and it involves Mercury’s orbit. Mercury has the most eccentric orbit of any planet—meaning that its orbit is noticeably elliptical and not as circular as the other planets. From Kepler’s Second Law (see “ The Solar System” article),3 a planet in an elliptical orbit moves faster when closer to the sun than it does when farther away.

The point of closest approach is called perihelion, and this is when Mercury moves the fastest. The most distant point is aphelion, and this is where it orbits the slowest. But Mercury’s rotation rate does not change. Interestingly, when Mercury is near perihelion, its rotation rate essentially matches its revolution rate, such that it keeps the same side pointed at the sun for several weeks.4 This configuration is very gravitationally stable.5 It would be strange to watch this phenomenon from the surface of Mercury itself—if we could somehow survive there. Imagine we begin by watching a very slow sunrise. It takes almost 20 hours between the first moment when the top of the sun peeks over the horizon and the time when the entire sun is visible. The sun seems enormous from Mercury’s perspective—appearing two and a half times larger in the sky than it does on Earth and over six times brighter! The sky remains black even when the sun is up, since Mercury lacks the comfort of Earth’s thick atmosphere. The sun then gradually climbs higher in the sky over the next several weeks. The stars also rise in the east, seeming to move at about twice the speed of the sun.

But as Mercury approaches perihelion, the sun seems to gradually slow its upward path, while the stars continue to rise and set at their usual pace. The sun is now noticeably larger than we witnessed at sunrise and over three times larger than it appears from Earth—and ten times brighter! Then the sun gradually comes to a complete stop and begins to travel slowly backward just slightly for about a week. We might feel like Hezekiah ( Isaiah 38:8 )!6 It then slows to a stop once again and reverses direction once more. The sun then gradually resumes its forward path, shrinking and fading a bit as Mercury moves toward aphelion. The sun eventually sets in the west, roughly three months after sunrise. Observing Mercury Since it is so close to the sun, Mercury appears quite bright in our nighttime sky, rivaling the brightest stars. Yet most people have never seen it. The planet can be a challenge to locate because it orbits so close to the sun and is easily lost in the glare. Most other planets can be seen late at night, when the sky is quite dark.

But not Mercury—it is only visible at twilight and only at certain times of the year when it is in a part of its orbit that appears (in angle) most distant from the sun. This position is called “greatest elongation.” At such times, it is possible to see Mercury just after sunset for “eastern elongations” or just before sunrise for “western elongations.”7 Thanks to Mercury’s short period, greatest elongations happen six (sometimes seven) times a year. Our next chance to see Mercury will be on October 9, 2013, or a few days before or after this. Go outside 20 to 30 minutes or so after sunset and look low to the west, just above the horizon. Venus will also be visible and bright and much higher in the sky. Look between Venus and the point where the sun sets and you will see the much-fainter Mercury. Mercury Confirms Creation Since Mercury is so close to the sun, and only visible low in the sky after sunset or before sunrise, Earth-based telescopic views of Mercury tend to be rather unimpressive and unrevealing.

That all changed when NASA sent the Mariner 10 spacecraft to visit Mercury in 1974. During several flyby encounters, Mariner 10 was able to image much of the day side of Mercury in unprecedented detail. It also measured a substantial magnetic field for this tiny planet. This is disturbing news for secularists who believe that our solar system is billions of years old, because a small planet like Mercury should not be able to maintain a magnetic field for so long. But this doesn’t surprise creationists. Physicist D. Russell Humphreys, Ph.D., has an interesting biblically based model that is able to account for the current strength of planetary magnetic fields based on their true age of about 6,000 years.8 His model lines up quite well with the current measured field strengths of the planets. Dr. Humphreys had also predicted that Mercury’s magnetic field will show measurable decay since the 1974 measurements. And this was confirmed by the more recent (2008-2013) Messenger spacecraft.9 Mercury has also been used to confirm other aspects of science.

Theoretical physicist Albert Einstein’s general theory of relativity indicates that gravitational fields affect the measurement of space and time. One such prediction of relativity is that Mercury’s perihelion should “precess” at a different rate than classical physics would predict. “Precess” means that the ellipse of Mercury’s orbit slowly rotates such that the angular location of the perihelion (and aphelion) gradually changes.10 Observations have confirmed Einstein’s prediction, bolstering our confidence in general relativity. Creationists have long debated when and how the craters we find in our solar system actually happened. Were the planets created with craters? Did God use some process to make the planets on Day Four such that the craters are the last material He brought to impact the surface? Did they happen after the Curse or during the Flood year? And if so, why? Mercury may also hold the key to theories of cratering. Most other rocky worlds in our solar system have tectonic, atmospheric, and volcanic activity that can remove evidence of any previous craters. But not Mercury. Its pristine surface may be a window into the original conditions of our solar system.11 What other secrets can we discern from this fascinating little world?

Time will tell. References To make this easier to understand, suppose that Mercury’s rotation and revolution periods were both exactly the same: 88 days. In this case, a person watching from a distant star would see Mercury rotate once in 88 days. But the sun would never see the other side of Mercury because the planet would keep its same “face” pointed toward the sun as it revolves around the sun. Likewise, a person standing on Mercury’s surface would never see a sunrise or sunset, if this were the case. The sidereal day would be 88 days, and the solar day would essentially be infinity. Since other planets also orbit the sun, their solar days are also different than their sidereal day. But the difference tends to be much smaller than with Mercury. Earth has only a four-minute difference between its solar and sidereal days. The reason Mercury exhibits such an enormous difference is because the length of its sidereal day is comparable to the length of its year. Lisle, J. P. 2013. The Solar System . Acts & Facts. 42 (6): 10-12.

At the time of perihelion, the orbital angular speed actually slightly exceeds the rotation angular speed for about one week. An observer on the surface would see the sun apparently move slightly backward in the sky for that one week. Some orbital resonances are stable and self-correcting, such as Mercury’s. Others are unstable, such that an orbiting body will be continually perturbed until it is ejected into a different orbit altogether. This appears to be the reason why there is a deficit of asteroids having simple resonances with Jupiter’s orbit. These resonance orbits are known as the Kirkwood gaps. Critics sometimes declare that God cannot do certain things, such as make the sun go backward as He did for Hezekiah. Such things are simply not possible, we are told. Yet this happens every three months on Mercury. It is probably not the same mechanism that God used for Hezekiah. Nonetheless, it is to the shame of those critics who attempt to tell God what He cannot do. “Eastern” denotes that Mercury is east of the sun. It therefore can be seen in our western sky just after sunset. Conversely, “western” elongations are those in which Mercury is farthest separated to the west of the sun.

At such a time, Mercury can be viewed in the eastern sky just before sunrise. Thomas, B. Mercury’s Fading Magnetic Field Fits Creation Model . Creation Science Update. Posted on icr.org October 30, 2011, accessed June 1, 2013. The perihelion distance does not change, only its angle. Imagine Mercury’s orbit lined up with a clock such that the perihelion is aligned with 12:00 and the aphelion is aligned with 6:00. As Mercury orbits the sun, the ellipse of its orbit slowly rotates counterclockwise such that at a later time perihelion would point to 11:30 and aphelion would point to 5:30. The precession of Mercury’s orbit is very slow, amounting to only 575 arc-seconds per century. Of this rate, 532 arc-seconds per century are due to gravitational perturbations of the other planets. The remaining 43 arc-seconds per century are due to the effects of general relativity. The agreement between the theoretical predictions and the observations is remarkable. 11.

This may also be true of the moon. Yet some creationists believe that the moon was impacted more recently by comets or a meteor stream in association with the Flood of Genesis 6 -8. It is unlikely that Mercury would have been strongly affected by the Flood due to its great distance. So differences between Mercury and the moon may help us understand better when these events occurred. * Dr. Lisle is Director of Physical Sciences at the Institute for Creation Research and received his Ph.D. in Astrophysics from the University of Colorado. Cite this article: Lisle, J. 2013. The Solar System: Mercury. Acts & Facts. 42 (8): 10-12. StarTeach Astronomy Education you are here > Our Solar System Our Solar System Our solar system consists of various bodies of different sizes which orbit the sun. The planets are the most important of these orbiting objects, and are arrayed in this order (first is closest to the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. The SUN, which is actually just an ordinary star, lies at the center of our solar system.

What makes the sun so special to us is simply the fact that it is so close to the Earth, only 93 million (92,960,000) miles away. This distance may seem huge, but when you realize that the closest star to us besides the sun is 25.3 trillion (25,300,000,000,000) miles away, you can see how giant space really is. Besides the obvious effects the sun has on our lives, solar activity also contributes to weather patterns on Earth. For instance, between the years 1640 and 1710, there were almost no sunspots on the surface of the sun. This coincided with a period of very cold weather on Earth known as the "Little Ice Age." Solar eclipses are particularly fascinating to watch. During a solar eclipse, the moon, the Earth, and the sun line up so that the moon lies between the sun and Earth. From our point of view on Earth, the sun is blocked completely by the moon for a few minutes. Another beautiful sight visible from Earth are the aurorae, or northern lights.

These brightly colored bands usually appear in the sky in locations near the north and south poles. The bright colors occur when high-energy particles from the sun are swept into our atmosphere and make the atoms there glow. The sun gets its energy from nuclear fusion, which is a nuclear process where four hydrogen atoms are converted into one helium atom. Since the total atomic mass of four hydrogen atoms is 0.7 percent more than the atomic mass of the helium atom, there is a little bit of extra mass left over at the end of this conversion process. In his famous E = mc^2 equation, Einstein proved that mass and energy are transferable. The extra mass created in the nuclear process described above is converted into energy. This nuclear fusion occurs in the central core of the sun, where the temperature is about 15 million degrees Fahrenheit and the pressure is 250 billion times the pressure of the Earth's atmosphere. MERCURY is the closest planet to the sun, and so it is also the fastest moving, orbiting the sun at 107,136 mph. This fast speed led the Romans to name it after Mercury, who was the speedy messenger of the Roman gods.

Since Mercury is so close to the sun, it is difficult to see from Earth. It is visible only right after sunset or right before sunrise. Mercury has no moons. Nearly 4,000 of the best photographs of Mercury were taken by the Mariner 10 space mission in 1974. Those pictures show that Mercury is a small rock that resembles the moon. However, it has long cliffs and shallow craters instead of the deep craters found on the moon. At the center of the planet is a large iron core. One year on Mercury is only 88 Earth days long, while one day on Mercury is equal to 59 days on Earth! This means that since Mercury has no atmosphere, and the sun shines continuously on the surface for 59 Earth days in a row, the daytime temperatures on Mercury can reach as high as 800 degrees Fahrenheit, under which conditions even metals such as lead would be melted! When it is nighttime on the surface, the temperature is -250 degrees Fahrenheit! VENUS is the closest planet to Earth, and is the third brightest object in our sky after the sun and moon.

Although it is similar to our planet in size, mass, and density, its surface environment is quite different. The atmosphere is made up of 96% carbon dioxide and small amounts of acids. One feature of the atmosphere is the greenhouse effect, in which heat (infrared radiation) is trapped near the surface because it gets reflected back down by the clouds. Venus is therefore very hot, approximately 900 degrees Fahrenheit. The surface has been studied by the Pioneer Venus 1 and Magellan spacecrafts, which used radar to peer through the clouds and make maps. They found that most of the surface is covered by craters and hills. There are also indications that Venus had a lot of volcanic activity in the past. The atmospheric pressure at the surface is 90 times Earth's pressure! Venus does not have any moons. Our planet, EARTH, is very unique. The environment is rich enough to support life, and many life forms thrive. Unlike any of the other planets, Earth is covered by vast quantities of water. In fact, more than 70% of the surface is under the ocean. Temperatures on Earth are very moderate compared to the other planets. Humans can live relatively comfortably at almost any location on the surface.

Our only moon is a quarter the size of Earth. It rotates on its axis at exactly the same rate that it orbits the Earth, and so we always see the same side of the moon. There is no air or water on the surface of the moon, and there is also no geological activity. The moon is the only other place in the universe that people have traveled to. MARS is a rocky red planet about half the size of Earth. It orbits the sun every 1.88 Earth years, and a day on Mars lasts about as long as one on Earth does. The planet's axis of rotation is also similar to the Earth's, which means that Mars experiences seasons as well. One unique feature is the polar ice caps, which are a combination of water ice and frozen carbon dioxide. The ice caps melt and rebuild according to the seasons, just as they do on Earth. The surface features on Mars are huge: the Valles Marinaris is a valley longer than the whole United States, and Olympus Mons is a volcano larger than Arizona and three times higher than the Hawaiian Island volcanoes. Three spacecraft have landed on Mars, and they have sent back pictures of a relatively flat surface covered with red rocks.

Mars has two moons, Phobos and Deimos, which are probably asteroids captured by Mars' orbit long ago. The ASTEROID BELT lies between Mars and Jupiter. The first asteroids, or minor planets, were discovered in the very early 1800s. Eventually over 4,000 of them were found. Astronomers had calculated that another planet should lie between Mars and Jupiter, and the asteroid belt seemed to solve this problem. Asteroids are composed of raw material from the creation of our solar system. For some reason, this material did not come together to form one planet. Asteroids are the source of most meteors that have hit the Earth. JUPITER is named after the king of the Roman gods. It is the largest planet, yet it spins very quickly on its axis- one day is about 10 Earth hours. The atmosphere is composed mainly of hydrogen and helium, although it is the small amounts of gases like ammonia and methane which make the bands on Jupiter look so colorful. It is very turbulent in the atmosphere, with huge storms frequently lasting years.

The Great Red Spot is a storm which has been in existence for 300 years, and covers an area larger than Earth! Jupiter is a gas giant with a very faint ring system. The atmosphere is so thick that it is impossible to see the rocky core that is probably at the center of this huge body. There are 16 moons orbiting Jupiter. The four brightest ones- Io, Europa, Ganymede, and Callisto- are visible from Earth through a small telescope. They were first discovered in 1610 by Galileo, who was using a telescope that he built. These four moons are therefore called the Galilean satellites. SATURN is one of the most beautiful and unusual sights in the sky. It is a giant gas planet about ten times the size of Earth. Its density is so low that it would float in a (very) big dish of water. Like Jupiter, Saturn has an atmosphere of hydrogen and helium and is often very stormy. The most unique feature of Saturn is its bright and colorful ring system, which is easily visible from Earth with a small telescope.

The rings are composed of billions of small rock and ice particles which reflect the sunlight and are held together by gravity and a few of Saturn's moons. The dark separation between the two main rings is called the Cassini division. Saturn has 18 moons. The largest is Titan, which is actually larger than Mercury and Pluto. URANUS was found in 1781 by the astronomer William Herschel. Like Saturn and Jupiter, Uranus is a gas giant with a helium and hydrogen atmosphere. Uranus has a faint ring system that cannot be seen from Earth except with a very large telescope. The rings were discovered only 23 years ago, when Uranus passed in front of a star, which appeared to blink as it passed the rings. Uranus has at least 15 moons, some of which are probably captured asteroids. NEPTUNE was discovered in 1846, after astronomers calculated where its orbit should be in order to cause strange motions in Uranus' orbit. Neptune's atmosphere is also composed of hydrogen and helium, and it has a very faint ring system that cannot be seen from Earth.

For 20 years out of every 248 years (one orbit of Pluto), Neptune is actually the farthest planet from the sun. This was the case from 1979 until 1999. Pluto is now once again the last planet in the solar system. Neptune has eight moons. PLUTO is usually (see 'Neptune' above) the farthest planet from the sun. It was found in 1930. Pluto is quite different from the other gas giants in the outer reaches of the solar system. In fact, it is simply a rock composed of frozen methane. There is an on-going debate about whether Pluto should be considered a planet, since it more closely resembles an asteroid or moon. Some astronomers believe that it is an escaped moon of Neptune, and others believe that it could be the remains of a large comet. Pluto is extremely cold, with a surface temperature of only about -360 degrees Fahrenheit. Pluto's only moon, Charon, was discovered in 1978. REFERENCES FOR THIS PAGE:

Question: Which planet in our solar system lies between Earth and Mercury?
Answer: Venus